1. Field of the Invention
The present application is directed to a method and device for radio communication between central and peripheral units of a traffic guidance system. The central and peripheral units communicate with one another via at least a first and second voice channel and at least a first and second data channel. The central unit includes a master terminal and the peripheral units include at least one of vehicles and passenger information systems. The central unit transmits messages to the peripheral units via the first data channel, and the peripheral units transmit responses to the central unit via the second data channel. The central and peripheral units also communicate via the first voice channel, and the peripheral units communicate with each other via the second voice channel when they are located at close range to each other.
2. Discussion of the Background Information
To ensure the smooth performance of medium and large scale transportation companies, in particular, in public commuter transportation, state-of-the-art computerized operating guidance systems are used as described in "Moderne Betriebsleitsysteme auf Basis von Datenfunknetzen" State-of-the-Art Operating Guidance Systems Based On Radio Data Networks! Verkehr und Technik, Special edition, Issue 12, Erich Schmidt Verlag, Berlin 1992 by Dr. J. Gehrig. Communication between the system units: the master terminal, vehicles and decentral control units, e.g., for influencing optical signal units which control the flow of traffic, is normally performed in real time via radio transmission. The point-to-point data transmission, for example, from a stationery point of the line to the vehicles, often takes place via IR connection. The radio network not only exchanges information between personnel at the master terminal and drivers, it also transmits information on optical and acoustical passenger at traffic junctions or stations. Conversations between personnel at the master terminal and/or the vehicles are usually transmitted analog via at least one voice channel. For controlling peripheral system units and for cyclic recording of actual operating data, digital messages are used which are converted into analog signals (modulation) and transmitted via at least one data channel. To optimize the procedure within the guidance system, decentral system-relevant information is retrieved and analyzed. Therefore, it is of importance to the master terminal to be in permanent contact with all system units, in particular, with the vehicles. In state-of-the-art traffic communication systems, preferably two data channels are provided between the central master terminal and the peripheral system units which enable permanent bi-directional radiocommunication. A radio set provided in the vehicles may, for example, receives and responds to the switching commands transmitted in the first channel of the master terminal, which, for example, contain a call request. After receiving a spontaneous call or request, a response message is immediately transmitted via the second channel from the vehicle to the master terminal. From the master terminal current data can be retrieved by the same method from the peripheral system units. Further, if necessary, the radio sets contained in these peripheral system units are instructed to switch to a specific channel, in order to set up a radiotelephone connection. After termination of the call, a signal is issued from the master terminal via the used voice channel, causing the radio set to make the radio connection again via the two data channels. Further, there is the possibility of switching the radio set to another voice channel on which voice signals can be exchanged between system units at close range over short distances.
The disadvantage with these known systems is that the radio sets provided in the peripheral system units are largely running to capacity as a result of the monitoring the polling messages (polling operation) transmitted in the first data channel and, therefore, are not available for further use. If the radio sets provided in the peripheral system units are used alternatively for the transmission of voice signals in the voice channels provided for said transmission, the polling messages transmitted via the first data channel can no longer monitored.